There are many double diaphragm pumps in the market that may be operated by compressed air or other pressurized fluid, generally these pumps may be classified into two sets:
a) Peripheral flow pumps that alternatively pump fluid from two fluid chambers positioned at the two outermost sides of the pump. Operating fluid chambers are separated by diaphragms from the pumped fluid chambers and these operating fluid chambers are on the inside of the diaphragms.
b) Central flow pumps that alternatively pump fluid from two fluid chambers positioned at either side of the central pump body. Operating fluid chambers are separated by diaphragms from the pumped fluid chambers and these operating fluid chambers are on the outside of the diaphragms.
Advantages of diaphragm pumps compared with other pump technologies include:                Versatility to pump a wide range of difficult to pump fluids due to, for example, being chemically aggressive or abrasive.        Take advantage of the operating fluid pressure, for example compressed air, to allow medium pressure fluids to be pumped and also for the control and operation of the pump.        Their design does not require the sealing systems used in rotary shaft pumps and that may leak.        
Peripheral flow diaphragm pumps are the most common kind of compressed air operated diaphragm pumps. The design of these pumps implies that the pumped fluid has to pass initially through an inlet manifold that includes one, or in most cases two, ninety degree elbows. After passing through this manifold the fluid has to enter into the fluid chambers from where it is discharged through a further manifold that also includes one, and in most cases two, ninety degree elbows. So, this design introduces pressure drops, an important factor in the low energy efficiency of these pumps.
The fluid path in a central flow pump does not circulate around the outside of the pump, so avoiding the associated pressure drops and improving the pump's efficiency. However, in most cases the design of the inlets and outlets towards and from the valves of the pumping chambers involves a complicated path. Also, ducts exist between the suction valves and the chamber inlet ports and between the chamber outlet ports and the discharge valves. The design of a pump that optimizes or eliminates these ducts would offer efficiency improvement.
Both peripheral flow pumps and central flow pumps use a directional valve to switch the flow of the operating fluid from one air chamber to the other. The switching time required causes a more or less pulsating flow. In a pumping system it is better to avoid pulsating flow for various reasons, for example to avoid: losses of efficiency, vibrations in the installation, irregular fluid supply, and loss of dosing accuracy.
Regarding the overall pumping performance, the suction pressure that is available to the pump is: suction pressure=(atmospheric pressure+fluid static pressure at the inlet)−(suction pressure that the pump is capable to generate). For this reason, any improvement in the suction capacity of the pump is of great value (an improvement of 0.1 bar in the discharge performance=approximately 0.1 bar over 5 bar of discharge pressure=“only” 2% of improvement, but an improvement of 0.1 bar in the suction performance=approximately 0.1 bar over 1 bar of suction height=10% improvement).
The diaphragms and check valves are essential components in all diaphragm pumps. Since they are in contact with the pumped fluid, they are available in different materials in order to maximize the pumps' range of application. Normally the diaphragms are fastened to the pump's central shaft using threaded connections and large discs, or pistons, that act on both the inside and outside of the diaphragms, to transmit the alternating driving forces to both diaphragms.
A significant factor during the working life of diaphragm pumps is the cost of maintenance. And important factors in this cost include: the cost to replace components at the end of their life (for example: diaphragms, check valves, directional valve and shaft), the labour time to service or substitute parts, and the downtime. Factors that reduce maintenance intervals are:                Diaphragms for chemically aggressive fluids, especially those with a design to achieve high chemical resistance not based only on elastomers, for example using PTFE, tend to rupture early due to the alternating movement during each cycle and the longer the stroke the shorter the life of such diaphragms.                    The accumulation of sediments in the pump fluid chambers can lead to wear of the diaphragms and shaft when the diaphragms are forced, due to contact with these deposits, to deform to finish their stroke.            Forces on the shaft and diaphragms when pumping against significant suction or discharge resistance.            Pumped fluids with solids in suspension cause increased wear of the diaphragms and check valves.            Contaminated compressed air can cause premature wear of the air valve.                        
Significant factors that increase the downtime and the labour time required to service or replace parts are:                The need to disconnect the pump from the fluid lines, when to access components requiring service or replacement, the inlet and outlet manifolds of the pump need to be disassembled.                    The need to disassemble the pump to access the components requiring service or replacement due to a design that does not facilitate access to these parts.                            When the pumped fluid is a dangerous fluid, then the disconnection of the fluid lines and the maintenance has to be realized with particular care to avoid spills and operator contact with the fluid.                                                
Should it be possible to increase the velocity of the stroke direction change over in a diaphragm pump and increase the cycling frequency, then this would reduce the negative effects of the fluid pulsations and it would be possible to reduce the stroke length, without reducing the flow rate, (flow rate=cycle frequency×volume pumped per cycle), and so increase diaphragm life. However, this requires a faster directional valve. Many designs of directional valves have evolved to reduce problems such as air leaks and/or poor operating reliability for pump starting and stopping. However, to reduce the air leaks, seals and lubricants are used that, unfortunately, may become contaminated and cause directional valve sticking and this can lead to pump start-up failures or undesired pump stopping. It is essential that a new directional valve does not leak air and delivers reliable pump start-up and running.
Various central flow pumps exist with the characteristics previously mentioned, for example EP-0823023/EP-1029185 and of special mention the pump EP-0132913 owned by FLOTRONICS AG. Such pumps comprise two chambers and four check valves, and a shaft that pushes the diaphragms. However, no pumps are known that incorporate all of the characteristics of the present invention comprising:                Check valves located in the centre of the pump that are accessible from above, with the suction valves at a different level than the discharge valves.        Fluid inlet ports to the chambers located above the shaft and within the chamber and fluid outlet ports from the chambers located below the shaft and within the chamber.                    A pivoting sealing member to distribute the air whose special protruding wing breaks the symmetrical functioning of the pump and so prevents the pivoting sealing member, and as a consequence prevents the pump, from stopping.                        A special diaphragm design.        Diaphragms assembled freely without any fastening to the shaft.        
Consequently, no pump is known that offers simultaneously all the innovations described and the functional advantages of the present invention.